Genetics Soap Opera - Serendip Studio's One World



Soap Opera Genetics – Genetics to Resolve Family ArgumentsHow could our baby be albino?Tiffany and Joe are shocked to learn that their new baby has albinism, with very pale skin and hair color. Tiffany‘s sister has come to visit her, so Joe goes out to talk with his sister, Vicky.Did Tiffany have an affair?Joe is very angry. He tells Vicky, "I think Tiffany had an affair with Sam! He’s the only albino we know. Obviously, Tiffany and I aren't albino, so Sam must be the father." Luckily, Vicky remembers her high school biology. She explains, “Two parents with normal skin and hair color can have an albino baby if both of them are heterozygous and have a recessive allele for albinism.” Joe exclaims, “You aren’t even speaking English! What do those words even mean?”1. To help Joe understand, explain the meaning of “heterozygous” and “recessive allele”.Once Joe understands these explanations, he asks, “So how do two parents who are not albino have a baby who is albino?” Vicky begins her answer by introducing these symbols:A = the dominant allele; a person who has the AA or Aa genotype has normal skin andhair color;a = the recessive allele; a person who has the aa genotype will have albinism, with very pale skin and hair.2a. Vicky explains that each heterozygous parent has the _______ genotype, so they will have (AA / Aa / aa)normal skin and hair coloring. Meiosis in a heterozygous parent can make eggs or sperm that have the A allele or the a allele.2b. Joe interrupts to ask, “What is meiosis?” Answer his question.2c. Vicki continues, “If an egg with the a allele is fertilized by a sperm with the a allele, then the zygote will have the _______ genotype, and this zygote will develop into a baby with albinism.” (AA / Aa / aa)2d. Joe asks “What is a zygote? How does the zygote develop into a baby with albinism?” Answer Joe’s questions.3. Joe asks “So, will all our children be albino?” Draw a Punnett square to answer Joe’s question. Put triangles around each symbol that represents the genetic makeup of an egg or sperm. Use arrows to illustrate an example of fertilization to produce a zygote.Circle the genotypes of any zygotes that would develop into an offspring who would have normal skin and hair coloring.Why don’t more babies have albinism?By now, Joe has calmed down and he is getting interested. He asks Vicky, "If that’s how it works, it seems as though a quarter of all babies should be albino. How come there are hardly any albino babies?" 4. What explanation should Vicky give to answer this question?Joe is starting to feel guilty for getting so mad. He says "Geez, I feel like a jerk. I should have known that Tiffany would never cheat on me." Vicky responds, "That's okay. You were upset. Let's just forget about it."Will Tiffany and Joe's next baby have albinism?Two years later, Tiffany is pregnant again, and she and Joe are discussing whether their second baby will be albino. Tiffany thinks the baby probably will be albino, but Joe remembers Vicky's explanation, and he tells Tiffany, "No, our second baby can't be albino because only one out of every four of our children should be albino. We already have one albino child, so our next three children should not be albino." 5a. Is Joe right? Explain why or why not.5b. What is the probability that Tiffany and Joe's second baby will have albinism?5c. How do you know? Were the babies switched?Two couples had babies on the same day in the same hospital. ? Denise and Earnest had a girl, Tonya. ? Danielle and Michael had twins, a boy, Michael, Jr., and a girl, Michelle. Tonya Michael Jr. MichelleDanielle was convinced that there had been a mix-up and she had the wrong baby girl. Tonya and Michael Jr. looked more like twins since they both had darker skin, while Michelle had lighter skin. Danielle said that the blood types of the babies and parents proved that there had been a mix-up. This figure shows the blood types of the families if the hospital did not make a mistake.This figure shows the blood types of the families if the baby girls were accidentally switched.1a. Based on the blood type evidence, do you think that the hospital made a mistake? yes ___ no ___1b. Explain why or why not.The Genetics of Blood TypesTo analyze the blood type evidence, you will need to understand the biology of blood types. Your blood type is determined by whether your red blood cells have type A and/or type B carbohydrate molecules on the surface. A Person With:Has:Type A blood Type A carbohydrate molecules on his or her red blood cellsType B blood Type B carbohydrate molecules on his or her red blood cellsType AB blood Both type A and type B carbohydrate molecules on his or her red blood cellsType O blood Neither type A nor type B carbohydrate molecules on his or her red blood cellsThe four different blood types result from three different alleles of a single gene in the DNA.These alleles give the directions for making different versions of a protein enzyme that can put different types of carbohydrate molecules on the surface of red blood cells.AlleleGives the directions for making a version of the enzyme that:EA puts type A carbohydrate molecules on the surface of red blood cellsEB puts type B carbohydrate molecules on the surface of red blood cellse is inactive; doesn't put either type of carbohydrate molecule on the surface of red blood cells Each person has two copies of the blood type gene, one inherited from his/her mother and the other inherited from his/her father. This table shows the relationships between some of the genotypes and blood types.GenotypeThis person's cells make: Blood TypeEAEA the version of the enzyme that puts type A carbohydrate molecules on the surface of red blood cells.Aee the inactive protein that does not put either type A or type B carbohydrate molecules on the surface of red blood cells.OEAe both the version of the enzyme that puts type A carbohydrate molecules on the surface of red blood cells and the inactive proteinA2. Explain why a person with the ee genotype has blood type O.3a. In a person with the EAe genotype, which allele is dominant? EA ___ or e ___ 3b. Explain your reasoning.4. For each genotype listed below, indicate whether the person’s cells would make each type of enzyme and which blood type would result.GenotypeWill this person's cells make the version of the enzyme that puts this carbohydrate on the surface of his/her red blood cells?Blood TypeEBEBtype A yes ___ no ___; type B yes ___ no ___; EBetype A yes ___ no ___; type B yes ___ no ___; EAEBtype A yes ___ no ___; type B yes ___ no ___;ABCodominance refers to inheritance in which two alleles of a gene each have a different observable effect on the phenotype of a heterozygous individual. Thus, in codominance, neither allele is recessive — both alleles are dominant. 5a. In the above table, circle the blood type that provides clear evidence of codominance.5b. Explain your reasoning. Were the babies switched? 6a. Use the symbols, EA, EB and e to write the possible genotypes for each parent and baby in the left-hand box immediately below.This figure shows the blood types of the families if the hospital did not make a mistake.This figure shows the blood types of the families if the baby girls were accidentally switched.6b. Draw a Punnett square for Michael and Danielle. Label the blood type for each potential offspring. 6c. Draw a Punnett Square to show how Earnest and Denise could have a child with type O blood.7a. Did the hospital make a mistake? Were the babies switched? yes ___ no ___7b. How do you know? Why do the twins look so different?Now, Danielle wants to know how her twins could look so different, with Michelle having light skin and Michael Jr. having dark skin. First, Danielle needs to understand that there are two types of twins. Identical twins have exactly the same genes, since identical twins originate when a developing embryo splits into two embryos. 8. How do you know that Michelle and Michael Jr. are not identical twins?Michelle and Michael Jr. are fraternal twins, which result when two different eggs are each fertilized by a different sperm. These different eggs and sperm can have different alleles of the genes that influence skin color.To begin to understand how Michelle could have light skin and her twin brother, Michael Jr., could have dark skin, we will consider two alleles of one of the genes for skin color.Notice that the heterozygous Tt individual has an intermediate phenotype, halfway between the two homozygous individuals (TT and tt). This is an example of incomplete dominance. GenotypePhenotype (skin color)TTdark brownTtlight browntttanIncomplete dominance occurs when the phenotype of a heterozygous individual is intermediate between the phenotypes of the two different types of homozygous individual. 9. Match each item in the list on the left with the best match from the list on the right.If the phenotype of a heterozygous individual:then the type of dominance is:? is intermediate between the phenotypes of the two different types of homozygous individuals, ___a. a dominant-recessive pair of alleles? is the same as the phenotype of an individual who is homozygous for the dominant allele, ___b. codominance? shows observable effects of both alleles, ___c. incomplete dominance10. The parents, Michael and Danielle, both have light brown skin and the Tt genotype. Draw a Punnett square and explain how these parents could have two babies with different color skin – one dark brown and the other tan.Obviously, people have many different skin colors, not just dark brown, light brown, or tan. This wide variety of skin colors results from the effects of multiple genes, plus environmental factors such as sun exposure. This flowchart shows how multiple genetic and environmental factors influence skin color.11. Use the information in the flowchart to explain how two people who both have the Tt genotype can have different skin colors – one lighter and one darker.I don't want my children to be color blind like me!Awilda and Frank at BreakfastAwilda: Are you sure you want to wear that new shirt to work today? A green and red shirt like that would be better for Christmas, not for St. Patrick's Day.Frank: Oh no! Not again! I really thought this shirt was just different shades of green. Where's the red?At Dinner That NightFrank: I’m worried that the baby we’re expecting will be color blind like me.Awilda: Remember, the doctor said that he doesn't think that any of our children will be color blind.Frank: I don't understand his reasoning. I'm color blind, so some of our children will probably be color blind like me.Awilda: The doctor said that, since no one in my extended family was color blind, I probably don’t have the allele for color blindness. Therefore, none of our children will be color blind.Frank: That doesn't make any sense. Neither of my parents is color blind, but I'm color blind. I think that some of our children will be color blind, since they will have a color blind father.Awilda recalls the doctor’s explanation. The X chromosome has a gene for color vision. The Y chromosome is much smaller and does not have this gene. XN represents an X chromosome with the dominant allele for normal color vision.Xcb represents an X chromosome with the recessive allele for color blindness.Awilda assumes that her genotype is XNXN. Answer the following questions to help Awilda explain to Frank why none of their children will be color blind. 1a. What is Frank’s genotype? XcbY ___ or XNY ___1b. How do you know?1c. Draw a Punnett square for Frank and Awilda. 1d. What will be the genotype of Frank and Awilda’s daughters? 1e. Why won’t their daughters be color blind?1f. Why won’t their sons be color blind?Frank: Okay, I guess I don't have to worry about any of our children being color blind, but what about our grandchildren? Couldn't some of them be color blind? Awilda: Well, some of our grandchildren could be color blind, especially some of our grandsons.Frank: I disagree. Girls have more X chromosomes than boys, so girls should be more likely to be color blind.2. Explain why the risk of color blindness is lower for females (with two X chromosomes) than for males (with only one X chromosome).Frank: Alright, I understand. My last question is “How could two parents who aren’t colorblind have a colorblind son like me?”3a. To answer Frank’s question, first give the genotype of Frank’s father.3b. How do you know?3c. What was the genotype of Frank’s mother?3d. How do you know?3e. Draw a Punnett square to show how two parents who are not color blind can have a color blind son. Circle the genotype of the colorblind son.4. A carrier is someone who does not have a condition (e.g., color blindness), but who can pass the condition on to his or her offspring. Explain why a woman can be a carrier for an X-linked recessive condition like color blindness, but a man cannot be a carrier for this condition. ................
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